Light beam transducer



United States Patent 6% lice 3,058,002 LIGHT BEAM TRANSDUCER Yro T.Sihvonen, Birmingham, Mich, assignor to General Motors Corporation,Detroit, Mich, a corporation of Delaware Filed Nov. 29, 1957, Ser. No.699,785 1 Claim. (Cl. 250-211) This invention relates to lighttransducing means and more particularly to means for elficientlyconverting light rays into electrical control currents.

Light sensitive materials used in control circuits for monitoring thecurrent flow therethrough dependent upon the amount of incident lightare of course in general use.

The present invention relates directly to the provision of a novel andhighly eflicient light transducing means.

It is an object in making this invention to provide a light transducerfabricated of semiconductive materials.

It is a further object in making this invention to provide a laminarphotosensitive light transducer formed of semiconductor elements.

It is a still further object in making this invention to provide alaminar assembly of semiconductor units for changing light rays intoelectrical control currents in which the rays are reflexed foramplification.

It is a yet further object in making this invention to provide a laminarlight sensitive body in which an electroluminescent section issandwiched between photoconductive sections to cause reflex action andamplify the response.

With these and other objects in view which will become apparent as thespecification proceeds, the invention will be best understood byreference to the following specification and claim and the illustrationsin the accompanying drawing in which:

FIGURE 1 is a diagrammatic showing of a light sensitive assemblyembodying my invention, and

FIGURE 2 is a similar figure showing a multiple unit transducer.

As indicated in the above general discussion the light transducer whichis the subject of the present invention is formed of a plurality ofsections which are fixedly secured together to provide a light sensitiveunit. Referring particularly to FIGURE 1, there is shown therein acompound light sensitive unit which consists of a first photoconductingsemiconductor unit 2 or layer which may be formed of any one of severaldifferent activated elements such as CdS, ZnS, PbS or CdTe. On onesurface of the layer 2 there is evaporated an electrode 4 for connectioninto an electrical circuit. To the opposite face of the layer 2 there issecured a layer of electroluminescent semiconductor 6. To the lower faceof electroluminescent layer 6 there is applied a second conductive layer8 which again may be a metallic film evaporated on the surface toprovide an electrical contact. Completing the laminar body is a secondlayer of photoconducting semiconductor 10 which may be formed of one ofthe other compounds mentioned above with regard to layer 2. Lastly, thelower face of layer 10 has a final conductive film 12 evaporated thereonto provide for electrical connection.

A battery 14 is connected across conductive layers 4 and 8 to apply adesired potential across that part of the laminar body formed ofphotoconducting layer 2 and 3,058,002 Patented Oct. 9, 1962electroluminescent layer 6. A second source of electrical powerindicated by battery 16 is connected in series with any suitable load 18and across the conductive films 8 and 12.

In the operation of this photosensitive assembly, light strikes the unitfrom the top as indicated by the arrow 20 passing down through thephotoconducting semiconductor layer 2 as indicated by the path 22. Itthen proceeds through the interface between layers 2 and 6 and on intothe electroluminescent semiconductor 6 which causes this toelectroluminesce and transmit waves of a certain color or wave lengthwhich waves are inclined to spread from the beam through the first layeras indicated by the arrows and the angled rays are reflected from theinterface 8 between layers 6 and 10 causing the rays to bounce back,induce new conductive areas 24 along the lower surface of thephotoconductive layer 2 and be reflected therefrom. These areas 24 inturn induce further electr0 luminescence of the electroluminescent layer6 thereby further increasing the total conductivity in the semiconductor10. This dispersion continues until most of the area of the lower partof the layer 2 is conducting and electroluminescent layer 6 glows inproportion to the intensity of the incident light beam 20. Each of theseadditional areas now induce additional conductivity columns such as 26,28 and 30 in the lower photoconducting layer 10 to amplify the responseof the total unit to the incident light. Naturally each of theseconductivity columns afiects the total flow of current I flowing throughthe load and thus a relatively weak beam of light can cause aconsiderable change in conductivity in the load circuit to control anydesired device.

FIGURE 2 illustrates the use of several of these laminar units in seriesto produce an even greater response. In that case the upper unitindicated as transducer 1 could be the same as that shown in detail inFIGURE 1 and comprising a photoconducting layer 2, an electroluminescentlayer 6 and a second photoconducting layer 10 all of which are bracketedand labeled transducer No. 1. However, in this case, photoconductinglayer 10 may also act as the upper photoconductive layer of a similarlaminar body labeled transducer No. 2. In that case it is alsoassociated with a second electroluminescent layer 32 and a thirdphotoconducting layer 34. Thus photoconducting layer 10 is common toboth transducers but the result is that a double effect is obtained bysuch construction. Proper bias voltages are applied through voltagesources 14, 16 and 36 and in this case, of course, the output signal orcontrol is taken off the conductive films 38 and 40 on opposite sides ofthe photoconductive layer 34.

It will thus be seen that this invention provides an efficient lightsensitive transducer for converting ambient light into control currentsor voltages.

I claim:

In photoelectric means for controlling a load, a source of light rayswhich vary in intensity, a laminated body one surface of which isexposed to the varying amounts of radiation from said source of lightrays, said laminar body including a first and a second outside layer ofphotoconducting material on opposite sides of a central layer ofelectroluminescent semiconductor material, said central layer ofelectroluminescent material when excited emitting light rays having awave length in the band con- 3 ducted by one of the photoconductingsemiconductor layers, means to apply an electric voltage across thefirst photoconducting and electroluminescent layer, a second voltagesupplying means, and circuit means connecting the second voltage supplymeans in series with the second photoconducting layer and the load whichis affected by the variations in the intensity in incident light.

De Forest et al Apr. 29, 1952 Briggs Oct. 26, 1954 41 Sheldon Mar. 20,1956 Ullery Dec. 11, 1956 Rosen Dec. 10, 1957 Halsted May 27, 1958Rothschild Dec. 1, 1959 Hanlet Mar. 22, 1960 Kazan June 21, 1960 OTHERREFERENCES Bube: Photoconductivity of Solids, 1960, John Wiley 10 &Sons, New York, pp. 229-235.

Hausmann & Slack: Physics, 2nd edition, August 1939, D. Van Nostrand,New York, pp. 609-617.

